1. Field of the Invention
The present invention relates to polyester fibers having excellent water absorbency, and more specifically, to polyester fibers having high water absorbency with high durability.
2. Description of the Prior Art
The term "water absorbency" of a fiber herein means the property to absorb water when the fiber takes the form of a fiber mass, yarn, strand, woven, knit or nonwoven fabrics or like fiber aggregate. To achieve this property, fibers should have a surface that is highly hydrophilic or wettable, but their individual filaments need not necessarily absorb or swell with water or moisture by themselves. Hydrophobic synthetic fibers, such as polyester fiber and polypropylene fiber, are literally hydrophobic and markedly inferior in water absorbency to cotton, regenerated cellulose fiber and the like, and have thus encountered problems when applied to uses requiring water absorbency. Attempts have therefore been made to increase the water absorbency of synthetic fibers while maintaining their excellent features such as good permanent setting property. So far, regretfully, water absorbency comparable to that of natural fibers has either not been obtained or, if obtained, was obtained only with such a sophisticated modifying process as to make the product too expensive to be widely used.
In recent years, fibers of polyesters, as represented by polyethylene terephthalate, have been playing increasingly important roles in textile uses, particularly as raw materials for nonwoven fabrics. Nonwoven fabrics have become widely used in the fields of sanitary applications, (e.g. disposable diapers, diaper liners and sanitary napkins, wipes for fast-food restaurants, household uses, (e.g. wipes and water-separating bags for the kitchen sink), medical uses, (e.g. base fabrics and fixing sheets for medical plasters, surgical gowns and masks, and the like). Durable water absorbency is desired, among the above uses for wipes and some sanitary applications.
Conventional hydrophilic polyester fibers are mostly provided with hydrophilicity by application of a finish onto their surface. Although these fibers exhibit hydrophilicity at the initial stage of their use, most of them rapidly lose the property during use due to removal of the finish from the surface.
When used for those nonwoven fabrics that are wet treated during their manufacturing process, the polyester fibers with initial hydrophilicity provided by application of a finish can, not provide the obtained fabrics with sufficient hydrophilicity because of loss of the finish during the wet treatment process.
Known are processes for providing polyester fiber with absorbency of water or moisture. Examples of these include incorporation of, polyethylene glycol or sodium dodecylbenzenesulfonate into the polyester constituting the fiber before spinning copolymerizing polyethylene glycol with polyester (see, Japanese Patent Application Laid-open No. 138617/1979). Fibers obtained by the above process of incorporation, however, display only initial water absorbency, with the level of hydrophilicity markedly decreasing with repeated washing. Furthermore, surface active agents such as sodium dodecylbenzenesulfonate are known to be toxic to humans and hence cannot be said to be suited for uses where the textiles containing them come into direct dermal contact with humans. Fibers obtained by the above process of copolymerization cannot exhibt water absorbency when the copolymerization ratio is small and, on the other hand, an increased ratio of the copolymerization component to give a satisfactory absorbency significantly adversely affects the other excellent properties inherent to polyester fiber. Accordingly, the above processes have failed in providng a polyester fiber having satisfactory water absorbent property.